examples: add example of running without grafana deployment

Signed-off-by: paulfantom <pawel@krupa.net.pl>

examples/grafana-only-dashboards.jsonnet

+local kp =
+  (import 'kube-prometheus/main.libsonnet') +
+  {
+    values+:: {
+      common+: {
+        namespace: 'monitoring',
+      },
+    },
+
+    // Disable all grafana-related objects apart from dashboards and datasource
+    grafana: {
+      dashboardSources:: {},
+      deployment:: {},
+      serviceAccount:: {},
+      serviceMonitor:: {},
+      service:: {},
+    },
+  };
+
+// Manifestation
+{
+  [component + '-' + resource + '.json']: kp[component][resource]
+  for component in std.objectFields(kp)
+  for resource in std.objectFields(kp[component])
+}